Ever more stringent statutory regulations regarding permissible emissions of harmful substances from motor vehicles in which internal combustion engines are arranged make it necessary to keep the emissions of harmful substances as low as possible during operation of the internal combustion engine. This can be done on the one hand by reducing the emissions of harmful substances which are produced during combustion of the air/fuel mixture in the respective cylinder of the internal combustion engine. On the other hand, exhaust gas post-treatment systems which convert the emissions of harmful substances that are produced during combustion of the air/fuel mixture in the respective cylinders into harmless substances are employed in internal combustion engines.
Avoiding the emission of soot particles in particular constitutes a major challenge which can be met for example by the provision of a suitable soot particle filter, which is however very costly.
In connection with internal combustion engines in which the injection valves are arranged such that they meter the fuel directly into the respective combustion chambers of the cylinders, it is advantageous to operate these as far as possible in a stratified charge mode in which the air/fuel mixture is stratified in a predefined area in the combustion chamber and the remaining areas only have a very low amount of fuel. In this manner, when the internal combustion engine is operating under partial load, a very high level of efficiency can be achieved. As a result of the nitrogen oxide emissions occurring during this stratified charge operation, a NOx catalytic converter is regularly provided in the case of such types of internal combustion engines which needs to be regularly regenerated again and this operation is supported by adopting a homogenous mode of operation with an enriched air/fuel ratio entering the combustion chamber of the cylinder. In the case of homogenous operation, the air/fuel mixture is distributed as homogeneously as possible throughout the entire combustion chamber of the cylinder.